Techniques for forming finFET transistors with same fin pitch and different source/drain epitaxy configurations

ABSTRACT

In one aspect, a method of forming a finFET device includes: partially forming fins in first/second regions of a substrate; selectively forming spacers on opposite sides of only the fins in a second region; completing formation of the fins such that, based on the spacers, the fins in the second region have a wider base; depositing an insulator between the fins; recessing the insulator to expose a top portion of the fins; forming at least one gate over the fins; further recessing the insulator in the source and drain regions to expose a bottom portion of the fins; and growing an epitaxial material in the source and drain regions that is un-merged in the first region yet is merged in the second region due to the base of the fins in the second region having a wider base. A finFET device is also provided.

FIELD OF THE INVENTION

The present invention relates to fin field-effect transistor (finFET)devices, and more particularly, to techniques for forming finFET deviceswith a same fin pitch but different source and drain epitaxyconfigurations.

BACKGROUND OF THE INVENTION

Fin field effect transistor (finFET) designs require a different numberof fins for different devices. For example, logic devices may needmultiple fins together to function as one transistor for high drivecurrent. In contrast, static random access memory (SRAM) may need onlyone fin per transistor to increase SRAM density.

For a same type of finFET transistor (e.g., an n-channel FET or nFET),the same epitaxial process is used to grow source/drain epitaxy. Forlogic transistors, it is desirable to have merged epitaxy. For SRAM,however, merged epitaxy is detrimental.

Using different fin pitches (tight fin pitch for merged epitaxy, andrelaxed fin pitch for un-merged epitaxy) can enable merged epitaxy andun-merged epitaxy. However, relaxed fin pitch comes with the drawback ofreduced transistor density.

Therefore, there is a need for forming finFET devices with mergedsource/drain epitaxy and un-merged source/drain epitaxy withoutdifferent fin pitches.

SUMMARY OF THE INVENTION

The present invention provides techniques for forming fin field-effecttransistor (finFET) devices with a same fin pitch but different sourceand drain epitaxy configurations. In one aspect of the invention, amethod of forming a finFET device is provided. The method includes:partially forming fins in a substrate, wherein at least one of the finsis formed in a first region of the substrate, and at least another oneof the fins is formed in a second region of the substrate; selectivelyforming spacers on opposite sides of only the fins in the second regionof the substrate; completing formation of the fins such that the fins inthe first region of the substrate have a uniform width and, based on thespacers, the fins in the second region of the substrate have a base thatis wider than the fins in the first region of the substrate; depositingan insulator between the fins; recessing the insulator to expose a topportion of the fins; forming at least one gate over a region of the finsthat serves as a channel region of the finFET device, and whereinregions of the fins extending out from under the gate serve as sourceand drain regions of the finFET device; further recessing the insulatorin the source and drain regions to expose a bottom portion of the fins;and growing an epitaxial material in the source and drain regions thatis un-merged in the first region of the substrate yet is merged in thesecond region of the substrate due to the base of the fins in the secondregion of the substrate being wider than the fins in the first region ofthe substrate.

In another aspect of the invention, a finFET device is provided. ThefinFET device includes: fins formed in a substrate, wherein at least oneof the fins is formed in a first region of the substrate and at leastanother one of the fins is formed in a second region of the substrate,wherein the fins in the first region of the substrate have a uniformwidth and the fins in the second region of the substrate have a basethat is wider than the fins in the first region of the substrate; aninsulator between the fins, wherein the insulator is recessed to exposea top portion of the fins in a channel region of the finFET device, andwherein the insulator is further recessed to expose a bottom portion ofthe fins in source and drain regions of the finFET device; at least onegate over the fins in the channel region; and an epitaxial material inthe source and drain regions that is un-merged in the first region ofthe substrate yet is merged in the second region of the substrate due tothe base of the fins in the second region of the substrate being widerthan the fins in the first region of the substrate.

A more complete understanding of the present invention, as well asfurther features and advantages of the present invention, will beobtained by reference to the following detailed description anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top-down diagram illustrating finFET transistors formedusing the present techniques having both un-merged and merged source anddrain regions, and a constant fin pitch according to an embodiment ofthe present invention;

FIG. 2A is a cross-sectional diagram illustrating a fin hardmask havingbeen formed on a substrate in the un-merged region of the substrateaccording to an embodiment of the present invention;

FIG. 2B is a cross-sectional diagram illustrating the fin hardmaskhaving been formed on the substrate in the merged region of thesubstrate according to an embodiment of the present invention;

FIG. 3A is a cross-sectional diagram illustrating the fin hardmaskhaving been used to pattern at least one fin in the un-merged epi regionof the substrate according to an embodiment of the present invention;

FIG. 3B is a cross-sectional diagram illustrating the fin hardmaskhaving been used to pattern at least one fin in the merged epi region ofthe substrate according to an embodiment of the present invention;

FIG. 4A is a cross-sectional diagram illustrating spacers having beenformed on opposite sides of the fins in the un-merged epi region of thesubstrate according to an embodiment of the present invention;

FIG. 4B is a cross-sectional diagram illustrating spacers having beenformed on opposite sides of the fins in the merged epi region of thesubstrate according to an embodiment of the present invention;

FIG. 5A is a cross-sectional diagram illustrating spacers (which areunmasked) having been removed from the fins in the un-merged epi regionof the substrate according to an embodiment of the present invention;

FIG. 5B is a cross-sectional diagram illustrating a mask having beenpatterned covering the spacers in the merged epi region of the substrateaccording to an embodiment of the present invention;

FIG. 6A is a cross-sectional diagram illustrating the fin etch havingbeen completed in the un-merged epi region of the substrate according toan embodiment of the present invention;

FIG. 6B is a cross-sectional diagram illustrating the mask having beenremoved and the fin etch having been completed with the spacers in placein the merged epi region of the substrate according to an embodiment ofthe present invention;

FIG. 7A is a cross-sectional diagram illustrating how the fins in theun-merged epi region of the substrate have a straight sidewall profileafter the fin etch according to an embodiment of the present invention;

FIG. 7B is a cross-sectional diagram illustrating how the fins in themerged epi region of the substrate have a stepped profile after the finetch and removal of the spacers according to an embodiment of thepresent invention;

FIG. 8A is a cross-sectional diagram illustrating a shallow trenchisolation (STI) oxide having been deposited over and between the fins inthe un-merged epi region of the substrate according to an embodiment ofthe present invention;

FIG. 8B is a cross-sectional diagram illustrating the STI oxide havingbeen deposited over and between the fins in the merged epi region of thesubstrate according to an embodiment of the present invention;

FIG. 9A is a cross-sectional diagram illustrating a recess etch havingbeen used to recess the STI oxide below the tops of the fins in theun-merged epi region of the substrate according to an embodiment of thepresent invention;

FIG. 9B is a cross-sectional diagram illustrating the recess etch havingbeen used to recess the STI oxide below the tops of the fins in themerged epi region of the substrate according to an embodiment of thepresent invention;

FIG. 10A is a top-down diagram illustrating at least one gate havingbeen formed over the fins in the channel region of the finFET devicesaccording to an embodiment of the present invention;

FIG. 10B is a cross-sectional diagram illustrating that the tops of thefins are exposed in the un-merged epi region of the substrate duringgate formation according to an embodiment of the present invention;

FIG. 10C is a cross-sectional diagram illustrating that the tops of thefins are exposed in the merged epi region of the substrate during gateformation according to an embodiment of the present invention;

FIG. 10D is a cross-sectional diagram through one of the gates accordingto an embodiment of the present invention;

FIG. 11A is a top-down diagram illustrating gate spacers having beenformed alongside the sidewalls of opposite sides of the gates accordingto an embodiment of the present invention;

FIG. 11B is a cross-sectional diagram illustrating further recessing ofthe STI oxide during the spacer etch in the un-merged epi region of thesubstrate according to an embodiment of the present invention;

FIG. 11C is a cross-sectional diagram illustrating further recessing ofthe STI oxide during the spacer etch in the merged epi region of thesubstrate according to an embodiment of the present invention;

FIG. 11D is a cross-sectional diagram through one of the gatesillustrating how the channel region of the fins is protected during thespacer etch according to an embodiment of the present invention;

FIG. 12A is a cross-sectional diagram illustrating source and drainregion epitaxy in the un-merged epi region of the substrate according toan embodiment of the present invention;

FIG. 12B is a cross-sectional diagram illustrating source and drainregion epitaxy in the merged epi region of the substrate according to anembodiment of the present invention; and

FIG. 12C is a cross-sectional diagram through one of the gates accordingto an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Provided herein are techniques for forming fin field effect transistor(finFET) devices having different source/drain epitaxy (i.e., un-mergedand merged source/drain epitaxy) using the same process and having thesame fin pitch. Advantageously, the present process enables theformation of finFET transistors for which it is desirable to have mergedepitaxy (such as with logic transistors) and those for which it isdesirable to have un-merged epitaxy (such as with SRAM) using the sameprocess. The process employs the same fin pitch for both types ofdevices, and therefore there are no density tradeoffs (see above).

An exemplary process flow implementing the present techniques forforming finFET transistors with a same fin pitch and differentsource/drain epitaxy configurations is now described by way of referenceto FIGS. 1-12. In general, a finFET includes a source region and a drainregion connected by at least one fin-shaped channel region. A gateregulates current flow through the channel. See, for example, FIG. 1.The channels in this example are beneath the gates. As shown in FIG. 1,the present techniques will be implemented in forming, during the sameprocess, finFET transistors having both merged and un-merged source anddrain regions. Namely, as will be described in detail below, epitaxy(“epi”) will be used to thicken the portions of the fins extending outfrom under the gates to form the source and drain regions of thetransistors. For one or more of the finFET transistors being formed,i.e., those in the “un-merged epi region,” the epitaxy will thicken butnot merge the fins in the source and drain regions, while at the sametime, for one or more of the other finFET transistors being formed,i.e., in the “merged epi region,” the epitaxy will merge the fins in thesource and drain regions. Advantageously, this is done with the finsbeing at the same pitch, therefore maximizing device layout density.

Reference will be made throughout the following description to thelayout shown in FIG. 1. For instance, cross-sectional depictions throughthe un-merged epi region will be along A-A′ and cross-sectionaldepictions through the merged epi regions will be along B-B′.Cross-sectional depictions through the gates will be along C-C′.

For instance, as shown in FIG. 2A (cross-section along A-A′) and FIG. 2B(cross-section along B-B′) the process begins with a substrate 202 inwhich at least one fin is to be patterned in the un-merged epi region ofthe substrate 202 and at least one fin is to be patterned in the mergedepi region of the substrate 202. While the example depicted in thefigures focuses on a bulk substrate (e.g., a bulk silicon (Si),germanium (Ge), silicon-germanium (SiGe), etc. substrate), the presenttechniques are not limited to any particular substrate configuration.For instance, alternatively a semiconductor-on-insulator (SOI) wafer maybe employed as the starting substrate. As is known in the art, a SOIwafer includes an SOI layer over a buried insulator. When the buriedinsulator is an oxide, it is often referred to as a buried oxide or BOX.

Next, a patterned fin hardmask 204 is formed on the substrate 202.Standard lithography and etching techniques can be used to form thepatterned fin hardmask 204. The patterned fin hardmask 204 marks thefootprint and location of the fins that will be patterned in thesubstrate 202. It is notable that the fin hardmask 204 has a constantpitch x in both the un-merged and merged epi regions of the substrate202, which will translate to the same constant pitch for the fins (to bepatterned). The term “pitch” as used herein refers to the distancebetween a point on one fin hardmask/fin to the same point on the nextadjacent fin hardmask/fin. As noted above, one could increase the pitchto prevent the epitaxy from merging the fins. There is, however, anundesirable tradeoff in terms of device density.

As shown in FIG. 3A (cross-section along A-A′) and FIG. 3B(cross-section along B-B′) the patterned fin hardmask 204 is then usedto pattern at least one fin 302 in the un-merged epi region of thesubstrate 202 and at least one fin 302 in the merged epi region of thesubstrate 202. This etch is a partial fin etch, meaning that at thisstage in the process only a top portion of the fins is formed in thesubstrate 202. This will permit selective processing of the fins in theun-merged versus those in the merged regions, after which the etching ofthe fins can be completed. See below.

Next, as shown in FIG. 4A (cross-section along A-A′) and FIG. 4B(cross-section along B-B′) spacers 402 are formed along the sidewalls onopposite sides of the fins 302. According to an exemplary embodiment,the spacers 402 are formed by depositing a suitable spacer material ontothe substrate 202 and surrounding the fins 302, and then patterning thespacer material into the individual spacers 402. Suitable spacersmaterials include, but are not limited to, oxide and nitride materials,such as silicon dioxide (SiO₂) and silicon nitride (SiN), respectively.

A selective masking and etching process is then used to remove thespacers 402 from the fins 302 in the un-merged epi region of thesubstrate 202 selective to those in the merged epi region of thesubstrate 202. Namely, following this selective masking and etchingprocess, the spacers 402 remain only along the sidewalls of the fins 302in the merged epi region of the substrate 202.

Specifically, as shown in FIG. 5A (cross-section along A-A′) and FIG. 5B(cross-section along B-B′) a mask 502 is patterned covering the fins302/spacers 402 in the merged epi region of the substrate 202. The mask502 can be formed using standard lithography and etching techniques. Thematerial used for the mask 502 should be such that the mask 502 can beremoved selective to the spacers 402. Namely, the process will nextinvolve removing the mask 502 while leaving the spacers 402 intact inthe merged epi region of the substrate 202. By way of example only, ifthe spacers 402 are formed from an oxide such as SiO₂, then the mask 502should be formed from a material that can be etched selective to anoxide, such as a nitride material (e.g., SiN).

As shown in FIGS. 5A and 5B, once the mask 502 is in place (andprotecting the spacers 402 in the merged epi region of the substrate202), the spacers 402 can then be removed from the fins 302 in theun-merged epi region of the substrate 202. As highlighted above, if thespacers 402 and the mask 502 are an oxide and nitride material,respectively, then an oxide-selective etch can be used to remove thespacers 402 from this select region of fins.

As shown in FIG. 6A (cross-section along A-A′) and FIG. 6B(cross-section along B-B′) following the selective removal of thespacers 402 from the fins 302 in the un-merged epi region of thesubstrate 202, the mask 502 is also removed. The result is the spacers402 remaining only alongside the fins 302 in the merged epi region ofthe substrate 202. Thus, via the above-described process, the spacers402 are selectively placed alongside the fins 302 in the merged epiregion of the substrate.

The fin etch is then completed. As noted above, the previous fin etchwas only a partial etch forming a top portion of the fins 302. As shownin FIGS. 6A and 6B, the fin hardmask 204 is still present on the fins inboth the un-merged and merged epi regions of the substrate 202. However,the spacers 402 are also present alongside the fins 302 in the mergedepi region of the substrate 202. Thus, the bottom portion of the fins302 (also referred to herein as the base of the fins 302) now etchedinto the substrate 202 have a different width in the un-merged versusmerged epi regions of the substrate 202 based on the extra masking widthprovided by the spacers 402 in the merged epi region. See FIGS. 6A and6B. It is notable however, that despite the difference in width of thefins 302 at their base, the pitch of the fins 302 has not changed, andremains the same between all of the fins 302. To use a simple example toillustrate this concept, if one were to measure pitch based on adistance from the center of one fin to the center of the next adjacentfin, then even if these fins have different widths, the location of thecenter of the fin remains the same.

The spacers 402 are then removed from the fins 302 in the merged epiregion of the substrate 202. See FIG. 7A (cross-section along A-A′) andFIG. 7B (cross-section along B-B′). As shown in FIG. 7A, followingcompletion of the fins etch, the fins 302 in the un-merged epi region ofthe substrate 202 have a straight sidewall profile. By contrast, asshown in FIG. 7B, the fins 302 in the merged epi region of the substrate202 have a stepped profile after fin etch completion due to theselective placement of the spacers 402 (see above). For instance, aftercompletion of the etch, the fins 302 in the merged epi region of thesubstrate 202 can have one width w at the top portion thereof, andanother width w′ at a bottom portion thereof, wherein w<w′. See FIG. 7B.The width w is the same width for the top and bottom portions of thefins 302 in the un-merged epi region of the substrate 202 (since the topportions of all of the fins are formed at the same time, and the fins302 in the un-merged epi region of the substrate 202 have a straightsidewall profile). See FIG. 7A.

To provide isolation for the fins 302, an insulator is deposited betweenthe fins 302. According to an exemplary embodiment, a shallow trenchisolation or STI process is employed whereby an STI oxide (e.g., silicondioxide (SiO₂)) is deposited over and between the fins 302 and thenrecessed to expose the fins. The result is an STI oxide surrounding thebase of each fin 302. Specifically, as shown in FIG. 8A (cross-sectionalong A-A′) and FIG. 8B (cross-section along B-B′), an STI oxide 802 isdeposited over and between the fins 302. Excess STI oxide 802 can beremoved using a process such as chemical mechanical polishing or CMP.The fin hardmask 204 remains covering and protecting the fins 302 duringthis process. As a result, the top of the STI oxide 802 is now coplanarwith the fin hardmask 204.

A recess etch is then used to recess the STI oxide 802 below the tops ofthe fins 302. See FIG. 9A (cross-section along A-A′) and FIG. 9B(cross-section along B-B′). An oxide-selective etch can be employed. Asa result of the recess etch, the STI oxide 802 is now presentcovering/separating the bottom portions of the fins 302. Notably, thestepped profile of the fins 302 in the merged epi region of thesubstrate remains buried in the STI oxide 802. Another way to look at itis that the profile of the fins exposed above the STI oxide 802 at thisstage in the process is the same (i.e., has the same width w—that of thetop portion of the fins 302 in both the un-merged epi and the merged epiregions of the substrate 202). This enables gate formation (see below)over a uniform fin shape. However, as will be described in detail below,further recessing of the STI oxide 802 can expose the stepped profile ofthe fins 302 in the merged epi region of the substrate 202 to enable theformation of merged source and drain region epitaxy in the devices inthat region. Further, to prepare the fins 302 for gate formation, thefin hardmask 204 can now be removed. See FIGS. 9A and 9B.

At least one gate 1002 is then formed over the fins 302 in the channelregion of the finFET devices. See FIG. 10A (top-down view), FIG. 10B(cross-section along A-A′), FIG. 10C (cross-section along B-B′), andFIG. 10D (cross-section along C-C′). Gate formation can includedepositing a suitable gate material or materials onto the fins 302, andthen using standard lithography and etching techniques to pattern thegate material(s) into the individual gates 1002.

As shown in FIG. 10A, according to an exemplary embodiment, the samegate line can cover the fins 302 in both the un-merged epi and mergedepi regions of the substrate 202. As such, a given gate line can serveas the gate 1002 for multiple finFET transistors, some having un-mergedsource and drain regions and others having merged source and drainregions, but wherein both devices have the same fin pitch.

The cross-section along A-A′ (FIG. 10B) and the cross-section along B-B′(FIG. 10C) are included to illustrate that the bottom portions of thefins (including the stepped fin profile in the merged region of thesubstrate 202) remain covered by the STI oxide 802 during the gateformation. As provided above, this enables gate formation over a uniformfin shape (i.e., fins of a uniform width w—that of the top portion ofthe fins 302 in both the un-merged epi and the merged epi regions of thesubstrate 202), and over fins of a uniform pitch x. This concept isfurther illustrated in FIG. 10D, which shows one of the gates 1002 nowpresent over the top portion of the fins 302 in both the un-merged epiand merged epi regions of the substrate 202.

Gate spacers 1102 are next formed alongside the sidewalls of oppositesides of the gates 1002. See FIG. 11A (top-down view), FIG. 11B(cross-section along A-A′), FIG. 11C (cross-section along B-B′), andFIG. 11D (cross-section along C-C′). To form the spacers 1102, asuitable spacer material is deposited onto the substrate 202 includingalong the sidewalls of the gates 1002, and then is removed (etched away)from the sidewalls of the fins 302 in the source and drain regions ofthe finFET devices (see FIG. 1). Suitable materials for spacers 1102include, but are not limited to, a nitride material such as siliconnitride (SiN). The spacer etch may be conducted using a directionaletching process such as reactive ion etching or RIE. As shown, e.g., inFIGS. 11B and 11C, during the spacer etch (which can be aggressive inorder to clear the spacer material from the fins in the source and drainregions), further recessing of the STI oxide 802 can occur in the sourceand drain regions. The channel region is however protected by the gates1002. See, e.g., FIG. 11D. As a result, the bottom portions of the fins302 are now exposed in the source and drain regions, including thestepped profile of the fins in the merged epi regions of the substrate.Namely, as shown in FIGS. 11B and 11C, following further recess of theSTI oxide 802 the exposed portions of the fins 302 (in the source anddrain regions) now have a different width in the un-merged epi (width w)versus merged epi (width w′) regions of the substrate 202. This willenable merging of the source and drain epitaxy in the select region ofthe substrate 202.

Namely, as shown in FIG. 12A (cross-section along A-A′), FIG. 12B(cross-section along B-B′), and FIG. 12C (cross-section along C-C′) theepitaxial material 1202 in the source and drain regions (see FIGS. 12Aand 12B) is grown on different shaped fins 302. As a result, theepitaxial material 1202 grown (i.e., same material grown by the sameprocess) will close the gap between the fins 302 in the merged epiregion of the substrate 202 (which has a greater width w′ wherein w′>w)before it would in the un-merged region of the substrate 202. As shownin FIG. 12C, the channel region is unaffected during the source anddrain region epi.

Although illustrative embodiments of the present invention have beendescribed herein, it is to be understood that the invention is notlimited to those precise embodiments, and that various other changes andmodifications may be made by one skilled in the art without departingfrom the scope of the invention.

What is claimed is:
 1. A method of forming a fin field-effect transistor(finFET) device, comprising: partially forming fins in a substrate,wherein at least one of the fins is formed in a first region of thesubstrate, and at least another one of the fins is formed in a secondregion of the substrate; selectively forming spacers on opposite sidesof only the fins in the second region of the substrate; completingformation of the fins such that the fins in the first region of thesubstrate have a uniform width and, based on the spacers, the fins inthe second region of the substrate have a base that is wider than thefins in the first region of the substrate; depositing an insulatorbetween the fins; recessing the insulator to expose a top portion of thefins; forming at least one gate over a region of the fins that serves asa channel region of the finFET device, and wherein regions of the finsextending out from under the gate serve as source and drain regions ofthe finFET device; further recessing the insulator in the source anddrain regions to expose a bottom portion of the fins; and growing anepitaxial material in the source and drain regions that is un-merged inthe first region of the substrate yet is merged in the second region ofthe substrate due to the base of the fins in the second region of thesubstrate being wider than the fins in the first region of thesubstrate, wherein the method further comprises: removing the spacersbefore depositing the insulator between the fins.
 2. The method of claim1, wherein the fins have a uniform pitch x.
 3. The method of claim 1,wherein the top portion of the fins in the second region of thesubstrate have a width w, and the bottom portion of the fins in thesecond region of the substrate have a width w′, wherein w′>w.
 4. Themethod of claim 3, wherein the top portion and the bottom portion of thefins in the first region of the substrate have the width w.
 5. Themethod of claim 1, further comprising: forming the spacers on oppositesides of the fins; forming a mask covering the spacers and fins in onlythe second region of the substrate; removing the spacers from the finsin the first region of the substrate; and removing the mask.
 6. Themethod of claim 1, wherein the spacers comprise oxide spacers.
 7. Themethod of claim 1, further comprising: forming gate spacers on oppositesides of the gate.
 8. The method of claim 7, further comprising:depositing a gate spacer material onto the substrate and alongside thegate; and removing the gate spacer material from the fins in the sourceand drain regions.
 9. The method of claim 8, wherein the gate spacermaterial comprises a nitride material.
 10. The method of claim 8,wherein the insulator is further recessed during removal of the gatespacer material from the fins.
 11. The method of claim 1, wherein theinsulator comprises an oxide material.